THE Versatile L-CARNITINE

The supplement L-carnitine finds numerous applications: from cardiovascular health to sports performance, it's a very versatile nutrient. The name "carnitine" is based on the Latin word for flesh: Caro or carnis. L-carnitine was first isolated from food—not surprisingly, a meat source—in the early 1900s.

At that time researchers suspected that L-carnitine played a role in muscle function; it would take many more decades before that relationship could be proved. Today, we know that L-carnitine is primarily found in body tissues that require high energy (such as the heart, skeletal muscles and the liver) where it plays a crucial role in the production of energy.

The body synthesizes most, if not all, of the L-carnitine it requires from the essential amino acids lysine and methionine, which is why this amino acid is considered conditionally essential. Although there are rare genetic diseases that can interfere with the body's production of L-carnitine, resulting in a primary deficiency of this amino acid, it is more likely for someone to have a "secondary" deficiency as a result of a disease (e.g., cirrhosis, chronic renal failure, diabetes, heart failure or Alzheimer's disease) or a medication side effect.

Long-chain fatty acids are the primary source of energy in the human body, and one of the most important things that L-carnitine does is to transport these long-chain fatty acids into the mitochondria, where they are used to create energy. L-carnitine then shuttles "acyl" groups back out of the mitochondria as they accumulate. Both of these jobs are vital for continued muscle activity. In fact, during high intensity exercise, the availability of L-carnitine might be a limiting factor. Studies in athletes indicate that supplementation with this nutrient might improve athletic performance, such as by lessening post exercise lactate levels and improving recovery from exercise stress.

Some research indicates that L-carnitine can counteract fatigue (presumably through its role in bringing fatty acids into the mitochondria to produce energy), although the bulk of the research in this area involves cancer patients and those with chronic fatigue syndrome. In one recent double-blind study, a group of 66 centenarians who were easily fatigued showed an increased capacity for physical and cognitive activity when supplemented with 2g daily of L-carnitine. Likewise, fatigue (which is common in celiac disease) lessened in a double-blind study of celiac patients supplemented with 2g daily of L-carnitine.

The heart muscle obviously requires constant access to energy to sustain its normal function. L-carnitine, by participating in the energy-creating process, has been shown to aid several cardiovascular-related conditions, including angina, congestive heart failure and peripheral artery disease.

Another area that L-carnitine supplements might help is for male infertility. Recently a review study reported that L-carnitine (or acetyl-L-carnitine) supplementation resulted in significantly improved pregnancy rate and better sperm motility in men affected by infertility.

L-carnitine might be helpful for weight control through its involvement in fat metabolism. Research with overweight people supplementing with 1g of L-carnitine daily for three months (while also engaged in diet and exercise changes) reported greater weight loss. However, other research has not found a beneficial effect of L-carnitine on weight loss.

Supplements of L-carnitine are safe in a wide range of doses, and for most health-promotion purposes recommended levels are from 1-3g daily. According to research published by the Council for Responsible Nutrition, evidence of safety for L-carnitine intake is very strong up to 2g daily. In addition, they point out that much higher levels have been tested without any side effects. The only exception is reports of an unpleasant fishy body odor at very high doses of L-carnitine.